18 May 2017

O.4.8.3 Transient Acoustic Signatures of the GreenHP with special focus on icing and defrosting

In the framework of the EU project GreenHP a new air-water-heat pump using the natural refrigerant
propane is developed. A new compressor concept, heat exchangers produced out of aluminium
microchannels attached to efficient air fin structures and a specialized fan have been implemented. The
acoustic behaviour is characterized setting a special focus on transient effects during icing and
defrosting. For this purpose, a 64-channel acoustic dome is positioned around the heat pump in the
climate chamber to acquire space-, time- and frequency resolved microphone data. Measurements are
performed for different acoustic shielding of the heat pump. The resulting acoustic directivity and its
variation during frosting is correlated to fluid flow and ice aggretion measurements: laser optical
methods (particle image velocimetry) and probe techniques (constant temperature anemometry) are
used to measure the air velocity both at the air inlet and in the gap between heat exchanger and fan.
Computational fluid mechanics is performed to simulate the frosting behaviour based on the measured
boundary conditions. For accessing the ice amount a local measuring method is applied based on the fact,
that the heat exchanger in the GreenHP is positioned horizontally: Below the heat exchanger area, 180
boxes are positioned gathering the water during defrosting. The local ice amount is compared to the
simulation results, which are correlated to the acoustic data. Providing these toolsets for development of
low noise signature air-to-water heat pumps is important for increasing acceptance of this technology.